In the process of manufacturing a nuclear fuel rod, a sealing plug is inserted into one end of an open-ended fuel tube. The nuclear fuel pellets then are inserted into the other, unsealed open end of the fuel tube. The open end of the fuel tube is plugged with a sealing plug having an orifice extending axially therethrough and communicating with the interior of the tube. The sealing plug is girth welded to the tube by welding around the outer circumference of the tube while concurrently evacuating the tube of gases produced during the girth welding process by drawing air outward through the axial opening in the sealing plug. After girth welding, the tube is pressurized by injecting inert gas through the axial opening into the tube. The axial opening then is seal-welded closed, thus forming a complete nuclear fuel rod.
Nuclear fuel rods typically are ultrasonically tested to detect flaws in the seal and girth welds. In the ultrasonic testing process, a nuclear fuel rod is advanced into a water tank and the end of the fuel rod is positioned against a rod stop member for precisely positioning the end of the fuel rod in the water tank. The ultrasonic testing equipment normally uses ultrasonic testing transducers for emitting sound waves. The transducers are highly sensitive and the end of the fuel rod must be precisely positioned in the water tank so that the transducers are positioned adjacent the end of the fuel rod and will emit sound waves directly onto the weld. Repetitive positioning of the fuel rods is important because the transducers are precisely positioned for emitting sound waves at a particular location.
Typically, repetitive positioning of fuel rods to within distances as little as 0.001 inch is necessary to assure that the seal welds of successive rods which are inserted into the water tank for testing will be properly ultrasonically tested. Positioning of the fuel rod for seal weld testing is critical because the seal weld is typically no more than 0.015 inches deep. That low weld depth requires precise positioning of the fuel rod to obtain adequate ultrasonic testing of the seal weld. The seal and girth welds are tested concurrently as the fuel rod is rotated and axially moved within the test tank. Positioning of the girth weld is not as important because as the fuel rod is advanced, it can be ultrasonically tested throughout the distance the fuel rod moves.
In a prior art rod positioning apparatus for use with ultrasonic testing of rods such as fuel rods, the fuel rod is moved into engagement with a rod stop member for positioning the end of a nuclear fuel rod for ultrasonic testing. In this prior art apparatus, the rod stop member includes an electrical contact sensor for sensing the end of the rod as it moves into a rod stop position on the rod stop member. The electrical contact sensor is connected by electrical wire leads to a controller which stops the fuel rod advancement and fixes the fuel rod in a rod testing position after the end of the fuel rod makes contact with the electrical sensor. After the rod is positioned, the rod stop member is lowered for allowing ultrasonic testing.
The apparatus as described does not provide for reliable repetitive positioning of successively advanced fuel rods. Because the electrical contact sensor is positioned in a water bath on the rod stop member, the water may affect adversely the reliability and operability of the sensor. Additionally, the water tends to corrode the electrical leads supplying current to the electrical contact sensor thus making operation of the apparatus unreliable.
The above prior art apparatus also does not provide for orienting a rod which is guided in an undesired orientation to the rod stop member. At times, a fuel rod is advanced into the water tank at an undesired orientation. Unless the fuel rod is oriented properly, the testing is not reliable. In this prior art apparatus, the rod stop member cannot orient a rod axially for proper positioning and ultrasonic testing. If the rod is advanced in a skewed direction relative to the rod stop member and the end of the fuel rod contacts the electrical contact sensor, the rod is locked into an undesired position.